Corrugating adhesive containing soluble high amylose starch

ABSTRACT

Corrugating adhesive compositions comprising soluble high amylose starch as the carrier starch may be prepared as a one-piece, dry mixture that can be dispersed in water at 25 degrees to 55 degrees C. and applied to paperboard without further preparation steps. The corrugating adhesives may be prepared without alkali, and used at any pH.

This application is a division of application Ser. No. 07/764,559 filedSep. 20, 1991 now U.S. Pat. No. 5,236,977, issued Aug. 17, 1993.

BACKGROUND OF THE INVENTION

This invention relates to a starch based corrugating adhesivecomposition containing soluble high amylose starch as the carrierstarch. The high amylose starch is rendered soluble before it is addedto the adhesive. The adhesive may be provided in the form of a "onepiece" dry mixture and used without first cooking the carrier starch inalkali. The use of alkali or borax in the dry mix is optional, and theadhesive is pH independent.

This invention also relates to a process for manufacturing corrugatedpaperboard employing a high amylose starch based corrugating adhesivethat is provided as a one piece dry mixture and prepared for use incorrugating by simply dispersing the dry mixture in water at 25° to 55°C.

The manufacture of corrugated paperboard usually involves a continuousprocess whereby a strip of paperboard is first corrugated by means ofheated, fluted rolls. The protruding tips on one side of this flutedpaperboard strip are then coated with an adhesive, and a flat sheet ofpaperboard, commonly known in the trade as a facing, is thereafterapplied to these tips. By applying heat and pressure to the twopaperboard strips, an adhesive bond is formed between the strips. Thisproduces a single-faced board in that the facing is applied to only onesurface. If a double-faced paperboard is desired, in which an innerfluted layer is sandwiched between two facings, a second operation isperformed wherein the adhesive is applied to the exposed tips of thesingle-faced board and the adhesive-coated tips are then pressed againsta second facing in the combining section of the corrugator under theinfluence of pressure and heat. The typical corrugating process and theuse of corrugators in general are described in U.S. Pat. Nos. 2,102,937and 2,051,025 to Bauer.

The particular adhesive employed in the corrugating process is selectedon the basis of several factors, including the type of bond required inthe box, package, or other item in which the finished corrugated productis to be used. Starch-based adhesives are most commonly used due totheir desirable adhesive properties and low cost.

The most commonly used starch based corrugating adhesives is an alkalineadhesive which is comprised of raw, ungelatinized starch (raw starch)suspended in an aqueous dispersion of cooked starch (carrier starch).The adhesive is produced by gelatinizing starch in water with sodiumhydroxide (or other alkali) to yield a primary mix of gelatinized orcooked carrier starch, which is then slowly added to a secondary mix ofraw starch, borax and water to produce the full-formulation adhesive. Inthe corrugating process, the adhesive is applied (usually at between 25°and 55° C.) to the tips of the fluted paper medium or single-facedboard, whereupon the application of heat causes the raw starch togelatinize, resulting in an instantaneous increase in viscosity andformation of the adhesive bond.

There are different theories regarding the respective roles of the rawand the carrier starches in the development of adhesive properties, butthere is substantial evidence to support the view that the carriercontributes to the bond strength and set speed of the adhesive, and thatgood tack in the carrier leads to good tack in the adhesive and,therefore, improved runnability in the full-formulation adhesive. (SeeR. Williams, C. Leake and M. Silano, TAPPI, Vol. 60 No. 4 April, 1977,pp. 86-89.)

It has been known for many years that a corrugated adhesive whosecarrier portion is prepared from a high amylose starch (i.e., at least40% amylose) is superior to one prepared from pearl starch, whichcontains about 27% amylose, because a carrier can be produced havingimproved rheological and film-forming properties, and increased moistureresistance. There are strong indications that the tack of the carrieralso plays an important role in the corrugating process. Furthermore,improvements in tack (green bond strength) permits higher corrugatingmachine speeds as compared to corrugating adhesives known in the priorart. Improved high amylose starch based corrugating adhesives aredisclosed in U.S. Pat. No. 4,787,937, issued Nov. 29, 1988, to Leake,which is hereby incorporated by reference.

U.S. Pat. No. 3,487,033, issued Dec. 30, 1969, to D. E. McElmury,describes a process for producing a single starch component adhesive byreaction of the ungelatinized starch in alkali and water in specifiedproportions and under heat conditions to provide a suspension of starchcontaining primarily ungelatinized starch in partially swollen form.This process requires complex preparation steps by the manufacturer ofcorrugated paperboard. In the absence of a crosslinking agent (e.g.,urea formaldehyde or a crosslinking resin), the adhesive prepared bythis process does not provide water resistance.

Commercial corrugating operators typically purchase the raw and carrierstarches, alkali and other adhesive components as separate items, thencook the carrier starch in alkali and water and, in a separate step, addthe raw starch and other components to the cooked carrier starch to formthe adhesive before running the corrugating operation. The alkali usedin cooking the carrier starch advantageously lowers the starchgelatinization temperature, and is particularly advantageous when highamylose starch is employed as the carrier starch. High amylose starchrequires a higher cooking temperature for gelatinization than otherstarches (e.g., in the absence of alkali, 135° to 170° C. is requiredfor high amylose starch versus 70° to 80° C. to gelatinize otherstarches). Without sufficient alkali, the high amylose carrier starchcannot be gelatinized by the corrugating operator using an atomosphericpressure cook. Cooking at greater than atmospheric pressure is needed.Thus, the alkali cook has become a highly desirable component of thestarch based corrugating adhesives known in the art, and an essentialcomponent of those adhesives comprising high amylose starch.

Smaller amounts of alkali are used as a component of conventional liquidadhesives that do not contain high amylose starch to optimize adhesiveperformance.

It has been discovered that by selection of certain soluble high amylosestarches that have been pregelatinized by an extrusion process, acoupled jet-cooking/spray-drying process, a steam-injection/atomizationspray-drying process, or other, similar processes, a pH independent,high amylose starch corrugating adhesive may be prepared and deliveredas a one-piece dry mixture. These soluble high amylose starches also maybe used separately to provide the carrier starch component of acorrugating adhesive without first cooking the starch in alkali. Thecarrier component can be prepared simply by dispersing the soluble highamylose starch in water at 25° to 55° C.

One-piece dry mixture have been used commercially, however, high amylosestarch has never been used in these mixtures. Until now, high amylosestarch could not be used effectively in a one-piece corrugating adhesivebecause of the extreme cooking conditions needed to disperse the highamylose starch.

Thus, the adhesives of this invention offer the convenience of a drymixture that can be dispersed in hot or cold water without cooking,independent of pH, together with the adhesive strength, waterresistance, higher corrugator speed and set speed and other benefitsassociated with high amylose starch. Because these adhesives can be usedwithout alkali, they exhibit better water resistance and do not requirethe use of a crosslinking agent to obtain a water resistant corrugatedpaperboard.

SUMMARY OF THE INVENTION

This invention provides a corrugating adhesive composition, comprisingan effective amount of a raw starch, and as a carrier starch, aneffective amount of a soluble high amylose starch, containing at least40% by weight of amylose, wherein the soluble high amylose starch is (a)a spray-dried, non-granular starch, characterized in that the starch issubstantially non-crystalline, substantially non-retrograded, and fullypre-dispersed; (b) a spray-dried uniformly gelatinized starch in theform of granular indented spheres, with at least a majority of thegranules being whole and unbroken, these starch granules being in theform of loosely-bound agglomerates or individual granules; or (c) anextruded, non-granular starch, characterized in that the starch is fullypre-dispersed; or (d) a mixture thereof, and an effective amount ofwater. Effective amounts include 60 to 95% raw starch, and 5 to 40% highamylose starch, based on the dry weight of the adhesive. To form theliquid adhesive, about 60-80% of water, based on the total weight of theadhesive, is added to the dry adhesive.

This invention provides a process for preparing corrugated paperboard,wherein the conventional step of cooking the high amylose carrier starchin alkali is eliminated.

This invention further provides a dry mixture of the corrugatingadhesive composition herein and a process for using this adhesive drymixture by merely dispersing it in hot or cold water prior toapplication to the paperboard.

The corrugating adhesive composition optionally contains alkali, borax,crosslinking agents, and other components traditionally used in starchbased corrugating adhesives.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The raw starch component of the adhesive may be derived from corn,potato, wheat, waxy maize, milo, or tapioca starch. Adhesives formulatedwith native high amylose starch as the raw starch can be used, butgenerally exhibit poorer tack and do not run as well in corrugation. Theraw starch component may be derived from modified ungelatinizedstarches, such as oxidized, converted and chemically derivatized (e.g.,starch ethers or esters) starches of the group described above.

The raw starch component may be used at concentrations of 60 to 95%,preferably 65 to 80%, based on the weight of the dry adhesive. Thecarrier starch component may be present at 5 to 40%, preferably 15 to25% of the dry adhesive.

The carrier component of the adhesive comprises a high amylose starch,i.e., a hybrid corn starch having an amylose content of at least 40%. Inthe alternative, blends of high amylose starches and other starcheshaving an amylose content below 40% are permissible. For purposesherein, the starch blend of the carrier component should contain atleast 40% and preferably 50% by weight of amylose, and the high amylosestarch (or blend thereof) employed as the carrier is used in an amountof from about 5 to 40% based on the weight of the dry adhesive.

Prior to use in the adhesive, the high amylose starch must be renderedsoluble in hot or cold water (e.g., at a water temperature of about 25°to 55° C., or higher). As used herein, "soluble" means that the starchin powdered form may be readily hydrated and dispersed in hot or coldwater or other aqueous medium to provide a starch solution in the formof a complex colloidal dispersion, rather than a true molecularsolution. One of three processes is preferably used to provide a fullygelatinized, fully functional high amylose starch: (1) an extrusionprocess; (2) a coupled jet-cooking/spray-drying process; or (3) asteam-injection/dual- or single-atomization spray-drying process.

In the first process, the extrusion process, the total moisture contentof the high amylose starch prior to extrusion should be at a level of21% or less by weight, based on the dry weight of the starch. Totalmoisture or water content includes both the residual moisture of thestarch, that is the amount picked up while stored at ambient conditions,and the amount of water fed to the extruder. Typically, starch, andparticularly high amylose starch, contains about 9 to 12% residualmoisture. Enough water must be present to allow the material to beprocessed, mixed and heated to the desired temperatures. While somewater may be added to the extruder, preferably only an amount which willbring the total moisture level to 21% or less is added. Accordingly,while the total moisture content that is used for carrying out theprocess may vary somewhat, depending on the actual material used andother process variations, a range of from about 10 to 21%, preferablyfrom about 13 to 19% and more preferably from about 14 to 17% by weight,will generally be suitable.

During the extrusion process, the temperature of the material in theextruder will be increased to reach about 150° to 250° C. Thistemperature must be maintained in at least the section of the extruderclosest to the die and just before the material leaves the extruder. Thedie is positioned at the point or location at the end of the extruderfrom which the extruded material exits the apparatus into the ambientair. Depending on the particular material being processed, as well asother process variations, this temperature can vary somewhat within thenoted range and preferably will be from about 160° to 210° C. Whenmodified starch such as a starch ether is used, the temperaturepreferably is form 160° to 180° C., whereas when an unmodified starch isused the preferred temperature is from about 170° to 210° C. in at leastthe section of the extruder closest to the die. By maintaining theseconditions in the extruder, the material upon leaving the die andextruder outlet into the open air, expands and cools to form an expandedcompressible starch product which can be ground to a particle sizesuitable for use in a corrugating adhesive.

The apparatus used in carrying out this process may be any screw-typeextruder. While a single- or twin-screw extruder may be used, it ispreferred to use a twin-screw extruder. Such extruders will typicallyhave rotating screws in a horizontal cylindrical barrel with an entryport mounted over one end and a shaping die mounted at the dischargeend. When twin screws are used, they may be corotating and intermeshingor nonintermeshing. Each screw will comprise a helical flight orthreaded section and typically will have a relatively deep feed sectionfollowed by a tapered transition section and a comparatively shallowconstant-depth meter section. The screws, which are motor driven,generally fit snugly into the cylinder or barrel to allow mixing,heating and shearing of the material as it passes through the extruder.

Control of the temperature along the length of the extruder barrel isimportant and is controlled in zones along the length of the screw. Heatexchange means, typically a passage, such as a channel, chamber or borelocated in the barrel wall, for circulating a heated media such as oil,or an electrical heater such as calrod or coil type heaters, is oftenused. Additionally, heat exchange means may also be placed in or alongthe shaft of the screw device.

Variations in any of the elements used in the extruder may be made asdesired in accordance with conventional design practices in the field. Afurther description of extrusion and typical design variations can befound in Encyclopedia of Polymer Science and Engineering, Vol. 6, 1986,pp. 571 to 631.

In the second process, a coupled jet-cooking/spray-drying process of thetype disclosed in U.S. Pat. No. 5,131,953, issued Jul. 21, 1992, toKasica, et al. and hereby incorporated by reference, is used togelatinize the high amylose starch. This process comprises the steps of:

(a) forming a slurry or a paste comprising the converted or unconvertedhigh amylose starch and water;

(b) jet-cooking the aqueous slurry or paste of the starch with steam ata temperature sufficient to fully disperse or solubilize the starch;

(c) conveying and introducing under high temperature and pressure thejet-cooked dispersion or solution into a nozzle of a spray-dryerchamber;

(d) atomizing the jet-cooked dispersion or solution through the nozzleof the spray-dryer;

(e) drying the atomized mist of the jet-cooked starch within thespray-dryer chamber; and

(f) recovering the jet-cooked and spray-dried starch as awater-dispersible or water-soluble powder.

The cooking temperature will depend upon whether a converted orunconverted starch is used. Typical temperatures are about 138°-177° C.(280°-350° F.).

The cooking chamber pressure used in the continuous coupled process islow, typically 20 to 130 psig, and is the saturation pressure of steamat the temperature used plus the small incremental pressure needed tomove the dispersion through the chamber. Cooking chamber pressuressuitable for high amylose starches are 80 to 150 psig, most preferably100 to 130 psig for a starch having an amylose content of about 70%.

An essential step in the above process is the conveying of thethoroughly cooked, substantially fully dispersed starch, under elevatedpressure and temperature, to the spray-dryer atomization nozzle. In thepreferred method, a low shear pneumatic nozzle is used, and the transferis carried out at substantially the same temperature and pressure usedin the jet cooking. The transfer is carried out without any venting tothe atmosphere. Atomization in a pneumatic nozzle may be used. Thepressure of the atomization gas (steam or air) used must be sufficientfor proper atomization into small droplets to allow rapid drying to anappropriate moisture without retrogradation.

Use of a pressure nozzle in the above process requires insertion of ahigh pressure pump (2,000 to 10,000 psig) between the jet-cooker andatomization nozzle. The temperature after passage through the highpressure pump should be maintained substantially equivalent to thejet-cooking chamber temperature. The pressure after the high pressurepump must be sufficient to properly atomize the cook to allow rapiddrying to an appropriate moisture without retrogradation.

These nozzles are described in detail on page 16f in Spray Drying: AnIntroduction to Principles, Operational Practice and Applications by K.Masters (Leonard Hill Books, London, 1972).

The spray-dried starch produced by the above process is non-granular andis characterized in that it is substantially non-crystalline andsubstantially non-retrograded.

In the third process, the steam-injection/dual- or single-atomizationcooking and spray-drying process of the type disclosed in U.S. Pat. No.4,280,851, issued Jul. 28, 1981, to Pitchon, et al., and herebyincorporated by reference, is used to gelatinize the high amylosestarch. In this process, a mixture of the granular starch is cooked orgelatinized in an atomized state. The starch which is to be cooked isinjected through an atomization aperture in a nozzle assembly to form arelatively finely-divided spray. A heating medium is also injectedthrough an aperture in the nozzle assembly into the spray of atomizedmaterial so as to heat the starch to a temperature effective togelatinize the starch. An enclosed chamber surrounds the atomization andheating medium injection apertures and defines a vent aperturepositioned to enable the heated spray of starch to exit the chamber. Thearrangement is such that the lapsed time between passage of the spray ofstarch through the chamber, i.e., from the atomization aperture andthrough the vent aperture defines the gelatinization time of the starch.The resulting spray-dried pregelatinized starch comprises uniformlygelatinized starch granules in the form of indented spheres, with amajority of the granules being whole and unbroken and swelling uponrehydration. Nozzles suitable for use in the preparation of thesestarches are described in U.S. Pat. No. 4,610,760, issued Sep. 9, 1986,to Kirkpatrick, et al., which is hereby incorporated by reference.

A steam-injection/single atomization process for cooking andspray-drying starch is disclosed in U.S. Pat. No. 5,149,799, issued Sep.22, 1992 to Rubens, which is hereby incorporated by reference.

Other processes may be used to gelatinize the high amylose starch,provided that the process selected yields one of the following products:(1) a spray-dried, non-granular starch, characterized in that the starchis substantially non-crystalline, substantially non-retrograded, andfully pre-dispersed; (2) a spray-dried, uniformly gelatinized starch inthe form of granular indented spheres, with at least a majority of thegranules being whole and unbroken, these starch granules being in theform of loosely-bound agglomerates or individual granules; or (3) anextruded, non-granular starch, characterized in that the starch is fullypre-dispersed; or (4) a mixture thereof. The soluble high amylosestarches described above, and combinations thereof, may be used as thecarrier starch in the corrugating adhesive without first cooking inalkali.

If the corrugating adhesive is formulated with alkali, the alkali (base)is preferably caustic soda, i.e., sodium hydroxide; however, other basesmay be employed in partial or full replacement of the sodium hydroxideand include, for example, alkali metal hydroxides such as potassiumhydroxide, alkaline earth hydroxides such as calcium hydroxide, alkalineearth oxides such as barium oxide, alkali metal carbonates such assodium carbonate, and alkali metal silicates such as sodium silicate.The alkali may be employed in aqueous or solid form.

If the corrugating adhesive is formulated with boron additives, theadditives may be selected from borax (sodium borate), the salts ofmetaborate (e.g., sodium metaborate), boric acid, and the like.Depending on the additive selected, the quantity of alkali, if present,may have to be adjusted to maintain a constant pH (e.g., more alkali isneeded for boric acid).

In a preferred embodiment, the dry adhesive is formulated to compriseabout 60 to 95% raw starch, 5 to 40% carrier starch (soluble highamylose starch), 0.5 to 6.0% alkali, and 0.5 to 8.0% borax. In anotherpreferred embodiment, the dry adhesive is formulated without borax tocomprise about 60 to 95% raw starch, 5 to 40% carrier starch and 0.5 to4.0% alkali. Conventional adhesives prepared using a separate alkalicook of native high amylose carrier starch require greaterconcentrations of alkali in the cook. In the presence of 0.5 to 6.0%alkali, on a dry adhesive weight basis, at the dilutions used herein,native high amylose starches will not gelatinize at 25° to 55° C.

In a one piece dry mix adhesive an alkali source other than sodiumhydroxide (e.g., sodium carbonate or calcium hydroxide) is preferred forstability during storage.

In an adhesive formulated without alkali, the adhesive has limited tackand is useful in applications where tack is not critical or wherealkalinity is harmful to items being stored in the paperboardmanufactured with the adhesive (e.g., glass items sensitive to etchingwith alkali). These lower pH adhesives comprising soluble high amylosestarch exhibit some water resistance.

Any effective combination of alkali and borax may be used, and anyconventional non-chemically functional additives may be incorporatedinto the adhesive herein in minor amounts, if desired. Such additivesinclude, for example, dispersants, scale inhibitors, wetting agents,proteins, plasticizers, solubilizing agents, rheology modifiers, waterconditioners, penetration control agents, peptizers such as urea,gelatinization temperature modifiers, inert fillers such as clay andfinely ground polymers, thickeners such as inorganic colloidal clays,guar, hydroxyethyl cellulose, alginates, polyvinyl alcohol, polymers ofethylene oxide and the like, wet strength resins and emulsions such aspolyvinyl acetate.

In the preparation of the corrugating adhesives herein, the preparationmethod used by the practitioner can vary without serious consequences.Unlike the adhesives known in the art, the adhesives of this inventionmay be prepared by dry blending the raw starch, carrier starch and,optionally, other components, dispersing the dry mix in water (usually60 to 80% water, based on the total weight of the adhesive), andmaintaining the adhesive at 25° to 55° C. during its application to thepaperboard. In alkaline systems a temperature of about 50° C. ispreferred. In neutral or acidic systems, a temperature of about 55° C.is preferred.

Optional ingredients, if desired, can be added at any convenient pointduring the preparation of either component but are usually added to thefinished adhesive.

The adhesive thus obtained can be used to bond single or double-facedboards using any equipment which is presently employed for thepreparation of corrugated board. Thus, the adhesive is maintained at atemperature preferably between 25° and 55° C. before its application tothe protruding tips of the fluted paper strip. The actual applicationmay be accomplished by the use of glue rolls which are ordinarilyemployed in most corrugating machines, or one may, if desired, utilizeother application methods which may be able to achieve an effectivedistribution of adhesive. Following the application of the adhesive tothe fluted paper strip, the latter is then brought into immediatecontact with the facing board under the influence of heat and pressure,as is well known in the art. A double-faced board may be subsequentlyprepared by bringing a second facing in contact with the open flutedsurface of the single-faced board by the usual procedures.

The examples which follow illustrate specific embodiments of theinvention. In the examples all parts and percentages are given by weightand all temperatures in degrees Fahrenheit and Celsius. All adhesiveformulations were prepared at a Stein Hall viscosity of 35 to 50seconds.

WATER SOLUBILITY MEASUREMENT A. Cold Water Solubility

The determination is carried out using distilled water at roomtemperature. About 0.5 g of starch is dispersed in 30-40 ml of water ina semi-micro stainless steel cup on a Waring blender base (Model31B292). The blender is run at low speed while the starch is added (allat once) and then run at high speed for 2 minutes. The dispersion isimmediately transferred to a 50 ml volumetric flask and diluted to 50 mlwith water. A 25 ml portion of the stock dispersion (shaken well toensure a homogenous dispersion) is removed by pipet and transferred to a50 ml centrifuge tube. The sample is spun down at 1800-2000 rpms for 15minutes. Once spun down, 12.5 ml of supernatant is pipetted into a 25 mlvolumetric flask, 5 ml of 5N potassium hydroxide (KOH) are added withswirling, and the mixture is diluted with water. The remainder of thestock dispersion is shaken well, the insoluble starch dispersed with 10ml of 5N KOH while swirling. The mixture is diluted to 50 ml with water.The optical rotation of both the concentrated stock solution and thesupernatant solution is measured. ##EQU1##

B. Hot Water Solubility

The procedure is the same as that described above except that boilingdistilled water at 90°-100° C. (194°-212° F.) is used for dispersing thestarch and all subsequent dilutions. No attempt is made to maintaintemperature during the procedure.

EXAMPLE 1

This example illustrates the preparation of high amylose starches thatare soluble in water at 25° to 55° C.

Part A Extrusion Process

A 70% amylose corn starch hybrid obtained from National Starch andChemical Company was fed into a Werner and Pfleiderer twin-screwco-rotating extruder, Model ZSK-30. The extruder was equipped with ascrew having a high shear screw design, a barrel diameter of 30 mm, twodie openings of 4 mm diameter each, a L/D of 21:1, and oil heatedbarrels. The starch was fed to the extruder at a screw speed of 250 rpmand a rate of 10 kg/hr with input moisture of about 9% based on weightof starch added (residual moisture of starting starch material was10-12%). The temperature in the extruder was increased to a level ofabout 200° C. in the barrel or section nearest the die and the extruderpressure was between 200-400 psi.

The product leaving the extruder was collected, allowed to cool, andground using a commercial multipass grinder (over 94% ground materialpassed through a 200 mesh U.S.T.M. screen). The product had a cold watersolubility of 35% and hot water solubility of 94%.

Part B Coupled Jet-Cooking/Spray-Drying Process

The variables used for the coupled jet-cooking/spray-drying processingof unmodified high amylose (about 70% amylose) corn starch are shownbelow, in Table I. A slurry of unmodified granular high amylose starchwas fed into a jet-cooker (Model C-15 available from National Starch andChemical Company). Steam was metered into the slurry to cook the starchand the cooked starch was conveyed to a pneumatic atomization nozzle topmounted in a 35 foot tall, 16 foot diameter Hensey spray-dryer. Steam at120 psig was used to atomize the starch. The atomized starch mist wasdried with air at 204° C. (400° F.).

                  TABLE I                                                         ______________________________________                                        Process Conditions for Jet Cooking/Spray Drying                               High Amylose Starch                                                                            Part A  Part B                                               ______________________________________                                        Slurry Solids      32.0%     26.2%                                            Cook Solids        28.0%     25.0%                                            Jet Cooking Temperature                                                                          143 (290) 163 (325)                                        °C. (°F.)                                                       Steam Flow         9.25 lb/min                                                                             --                                               Cook Flow          3.8 gal/min                                                                             6.5 gal/min                                      Nozzle Type.sup.a  1J-152    1J-152                                           Dryer Inlet Temp °C. (°F.)                                                         230-191   230-191                                                             (446-375) (446-375)                                        Dryer Outlet Temp °C. (°F.)                                                        82-96     82-96                                                               (180-205) (180-205)                                        Atomizing Steam (psig)                                                                           120       120                                              ______________________________________                                         .sup.a Pneumatic nozzle obtained from Spraying System, Inc. (Model 1J;        twofluid).                                                               

The cold water solubility of the non-granular starch powder was 97.4%and the hot water solubility was greater than 99%.

Under process conditions shown above, in Table I, a converted highamylose corn starch (about 70% amylose) was processed using the coupledjet-cooking/spray-drying process. A slurry of the starch was treatedwith 2.5% hydrochloric acid at 52° C. (126° F.) for 16 hours to give aconverted starch having a calcium chloride viscosity of 25 seconds.After neutralization with sodium carbonate to a pH of about 6, thegranular converted starch was filtered, washed and dried. The starch wasthen jet-cooked, and the jet-cooked starch dispersion was conveyed to apneumatic atomization nozzle top mounted in a 35 foot tall, 16 footdiameter Hensey spray-dryer. The atomized starch mist was dried with airat 204° C. (400° F.).

The converted starch powder was 93.0% soluble in cold water and 97.1%soluble in hot water.

Part C Steam-Injection/Dual-Atomization or Single Atomization Process

Unmodified granular corn starch containing about 70% amylose wasslurried in water at 33.7% solids. This slurry was pumped by a Matt andGaulin triplex pump at about 2.4 gallons per minute under about 5,000psig to three steam atomization nozzles (dual-atomization nozzles asdescribed in FIG. 1 of U.S. Pat. No. 4,280,851, issued Jul. 28, 1981, toPitchon, et al.), mounted at the top of a 35 foot tall, 16 foot diameterHensey spray-dryer. Steam at about 154 psig was used to gelatinize andatomize the starch. Air at 230° C. (445° F.) was used to dry theatomized starch mist.

The recovered granular pregelatinized starch powder had a cold watersolubility of about 83 percent and a hot water solubility of about 95percent.

EXAMPLE 2

This example illustrates the preparation of premixed alkaline one-piececorrugating adhesives using the cold water soluble high amylose starchesdescribed above as the carrier starch.

The following components were dry mixed:

    ______________________________________                                        Dry Mixture Corrugating Adhesive I                                            Components.sup.c Percent  Grams                                               ______________________________________                                        Corn starch.sup.a                                                                              20.40      800.00                                            Pearl corn starch.sup.b                                                                        71.40    2,800.00                                            Sodium Metaborate                                                                               3.62      142.00                                            Calcium Hydroxide                                                                               1.88      74.00                                             Sodium Carbonate  2.70      106.00                                                             100.00   3,922.00                                            ______________________________________                                         .sup.a Corn starch hybrid containing 70% amylose and solubilized by the       methods of Example I, above.                                                  .sup.b Corn starch containing about 27% amylose that was obtained from        National Starch and Chemical Company.                                         .sup.c When a crosslinker was used, it was added at 200 g/3,922 g of dry      mix corrugating adhesive (4.85%) for a total dry mix of 4,122 g.         

A total of 9,805 grams of water at 38° C. (100° F.) was placed in thesecondary mixer of a Henry-Pratt adhesive mixer, 3,922 grams of theabove dry mixture were added, and this dispersion was mixed for 20minutes.

A total of 200 grams of a modified ketone-aldehyde resin (Dacrez®crosslinker, obtained from National Starch and Chemical Company) (at1.4% of total adhesive) was then mixed into the adhesive.

A control was prepared in the conventional manner using a two-stageprocess. In the primary mixer of a Henry-Pratt adhesive mixer, 1,200 gof a raw corn starch hybrid containing 70% amylose was cooked at 54° C.(130° F.) for 15 to 20 minutes in 2,502 g of water containing 114 g ofsodium hydroxide (that had been pre-dispersed in 250.2 g of water).After cooking, 2,502 g of water at room temperature was added to thestarch. In the secondary mixer, 7,756 g of water was heated to 32° C.(90° F.) and 4200 g of raw corn starch and 72 g of 5 mole borax wasadded to the water. The contents of the primary mixer then were droppedinto the secondary mixer and blended to form the adhesive.

Single face corrugated board was then made with this adhesive on a onefoot wide pilot corrugator at 250 feet per minute. Application roll gapsettings were adjusted to vary the adhesive pickup. The resulting boardwas evaluated for adhesive strength (pin test) using a Hinde and Dauchcrush tester under two test conditions: dry 24 hours after manufacture(dry pin); and wet after 24 hours submerged in room temperature tapwater (wet pin). Board construction was 69 lbs/MSF (thousand square feetof board) wet strength liner and 33 lbs/MSF wet strength medium. Sampleswere cut into 2"×4" pieces (8 in²) for pin adhesion testing.

                  TABLE II                                                        ______________________________________                                        Corrugating Adhesive Strength Test                                                                      Dry Pins Wet Pins                                                  Pickup     (lb/8    (lb/8                                      Carrier Starch.sup.a                                                                         lbs/MSF.sup.b                                                                            in.sup.2)                                                                              in.sup.2)                                  ______________________________________                                        Jet-Cooking/Spray-Drying                                                                     1.0        131      8.5                                        Process of Part B                                                                            2.0        144      9.5                                                       2.5        147      10.2                                       Steam          1.0        132      9.9                                        Injection/Atomization                                                                        2.0        147      11.3                                       Process of Part C                                                                            2.5        148      11.8                                       Extrusion      1.0        120      8.2                                        Process of Part A                                                                            2.0        141      10.5                                                      2.5        147      11.4                                       Extrusion      1.0        120      0                                          Process of Part A                                                                            2.0        134      0                                          No Crosslinker.sup.d                                                                         2.5        137      0                                          Conventional Cook                                                                            1.0        120      12.0                                       Control        2.0        134      16.5                                                      2.5        137      17.7                                       ______________________________________                                         .sup.a Carrier starches contained 70% amylose and were solubilized by the     methods of Example 1, Parts A, B and C.                                       .sup.b MSF = Thousand square feet of board.                                   .sup.c Lb/8 in.sup.2 is based on sample size of 2" × 4".                .sup.da See Example 4, below.                                            

These results show that the soluble high amylose starches prepared bythe three methods of Example 1 can be used to formulate one piece, drymixture corrugating adhesives which were easily prepared in conventionalequipment, provided good dry strength, formulated well with conventionalwet strength resins, and were readily applied using conventionalcorrugating equipment.

EXAMPLE 3

This example illustrates the use of soluble high amylose starches as acarrier starch in a corrugating adhesive prepared without alkali.

The adhesive was prepared and tested as in Example 2, using thefollowing adhesive formulation.

    ______________________________________                                        Dry Mixture Corrugating Adhesive II                                           Components.sup.c Percent  Grams                                               ______________________________________                                        Corn starch.sup.a                                                                              16.20      600.00                                            Pearl corn starch.sup.b                                                                        76.00    2,800.00                                            Sodium Metaborate                                                                               7.70      282.00                                                             99.90    3,682.00                                            Water                     9,580.00                                            Crosslinker.sup.c           200.00                                            ______________________________________                                         .sup.a Corn starch hybrid containing 70% amylose and solubilized by the       method of Example 1, Part C, above.                                           .sup.b Corn starch containing about 27% amylose that was obtained from        National Starch and Chemical Company.                                         .sup.c A modified ketonealdehyde resin (Dacrez ® crosslinker, obtaine     from National Starch and Chemical Company).                              

The crosslinker was added to the water before blending the water and drymixture. The alkali-free adhesive strength test results were:

dry pins=132 lbs/8 in²

wet pins=4.5 lbs/8 in²

at a pickup of 1.5 lbs/MSF.

Thus, an acceptable, alkali-free corrugating adhesive was prepared froma one piece mixture containing soluble high amylose starch as thecarrier starch.

EXAMPLE 4

This example illustrates the use of soluble high amylose starches as acarrier starch in a corrugating adhesive prepared without a crosslinkingagent.

The extrusion process of Example 1, Part A, was used to solubilize a 70%amylose corn starch. The adhesive formulation of Example 2 was preparedas in Example 2, except that no crosslinker was added. Results indicatedthat a satisfactory adhesive was obtained without a crosslinker (seeTable II).

EXAMPLE 5

This example illustrates the use of soluble high amylose starches as acarrier starch in a corrugating adhesive prepared without alkali orborax.

The following components are dry mixed:

    ______________________________________                                        Dry Mixture Corrugating Adhesive                                                             Percent                                                        ______________________________________                                        Corn starch.sup.a                                                                              19.72                                                        Pearl corn starch.sup.b                                                                        75.83                                                        ______________________________________                                         .sup.a Corn starch hybrid containing 70% amylose and solubilized by the       methods of Example 1, above.                                                  .sup.b Corn starch containing about 27% amylose obtained from National        Starch and Chemical company.                                             

A total of 7,020 grams of water at 38° C. (100° F.) is placed in thesecondary mixer of a Henry-Pratt adhesive mixer, 3,000 grams of theabove dry mixture are added, and this dispersion is mixed for 20minutes.

Single face corrugated board is made on a one foot wide pilot corrugatorat 250 fpm. Application roll gap settings are adjusted to vary theadhesive pickup. The resulting board is evaluated for adhesive strength.

These results show that the soluble high amylose starches prepared bythe three methods of Example 1 can be used to formulate one piece drymix corrugating adhesives without alkali or borax. These adhesives areeasily prepared in conventional equipment, provide the strength andwater resistance typical of high amylose containing adhesives, formulatewell with conventional wet strength resins, and can be readily appliedusing conventional corrugating equipment.

Now that the preferred embodiments of the present invention have beendescribed in detail, various modifications and improvements thereon willbecome readily apparent to those skilled in the art. Accordingly thespirit and scope of the present invention is to be limited only by theappended claims, and not by the foregoing disclosure.

We claim:
 1. A process for preparing a corrugated paperboard, comprisingthe steps:a) providing a dry mixture for use as a corrugating adhesive,comprising an effective amount of a raw starch and an effective amountof a soluble high amylose starch, having at least 40% amylose, whereinthe soluble high amylose starch is selected from the group consisting of(a) a spray-dried, non-granular starch, characterized in that the starchis substantially non-crystalline, substantially non-retrograded, andfully pre-dispersed; (b) a spray-dried, uniformly gelatinized starch inthe form of granular indented spheres, with at least a majority of thegranules being whole and unbroken, these starch granules being in theform of loosely-bound agglomerates and individual granules; and (c) anextruded, non-granular starch, characterized in that the starch is fullypre-dispersed; and (d) a mixture thereof, and wherein the soluble highamylose starch is substantially water soluble at 25° to 55° C. in theabsence of alkali; b) preparing a corrugating adhesive by blending thedry mixture with 60 to 80% water, based on the total weight of theadhesive; c) applying the corrugating adhesive to the tips of thecorrugations of a fluted paper strip; and d) applying a facing to theadhesive coated tips of said fluted paper strip to form an adhesivebond, wherein the process is carried out at any pH and the corrugatedpaperboard produced by this process is characterized by waterresistance.
 2. A process for preparing a corrugated paperboard,comprising the steps:a) preparing a corrugating adhesive composition,comprising an effective amount of a raw starch, an effective amount ofwater, and an effective amount of a soluble high amylose starch, havingat least 40% by weight of amylose, wherein the soluble high amylosestarch is selected from the group consisting of (a) a spray-dried,non-granular starch, characterized in that the starch is substantiallynon-crystalline, substantially non-retrograded, and fully pre-dispersed;(b) a spray-dried, uniformly gelatinized starch in the form of granularindented spheres, with at least a majority of the granules being wholeand unbroken, these starch granules being in the form of loosely-boundagglomerates and individual granules; and (c) an extruded, non-granularstarch, characterized in that the starch is fully pre-dispersed; and (d)a mixture thereof, and wherein the soluble high amylose starch issubstantially water soluble at 25° to 55° C. in the absence of alkali.b) applying the corrugating adhesive to the tips of the corrugations ofa fluted paper strip at 25° to 55° C.; and c) applying a facing to theadhesive coated tips of said fluted paper strip to form an adhesivebond, wherein the process is carried out at any pH and the corrugatedpaperboard produced by this process is characterized by waterresistance.
 3. The dry mixture of claim 1, wherein the dry mixturefurther comprises an effective amount of alkali and an effective amountof borax.
 4. The dry mixture of claim 3, wherein the dry mixturecomprises about 60 to 95% of a raw starch, about 5 to 40% of the solublehigh amylose starch, about 0.5 to 6.0% alkali, and about 0.5 to 8.0%borax, based on the dry weight of the adhesive.
 5. The dry mixture ofclaim 1, wherein the dry mixture further comprises an effective amountof alkali.
 6. The dry mixture of claim 5, wherein the dry mixturecomprises 60 to 95% of a raw starch, 5 to 40% of the soluble highamylose starch, and 0.5 to 6.0% alkali, based on the dry weight of theadhesive.
 7. The dry mixture of claim 1, wherein the dry mixture furthercomprises an effective amount of borax.
 8. The dry mixture of claim 7,wherein the dry mixture comprises 60 to 95% of a raw starch, 5 to 40% ofthe soluble high amylose starch, and 0.5 to 8.0% borax, based on the dryweight of the adhesive.
 9. The dry mixture of claim 1, furthercomprising a crosslinking agent.
 10. The dry mixture of claim 9, whereinthe crosslinking agent is a ketone-aldehyde resin.
 11. The corrugatingadhesive of claim 2, wherein the adhesive further comprises an effectiveamount of alkali and an effective amount of borax.
 12. The corrugatingadhesive of claim 11, wherein the adhesive comprises about 60 to 95% rawstarch, 5 to 40% soluble high amylose starch, 0.5 to 8.0% borax, and 0.5to 6.0% alkali, based on the dry weight of the adhesive.
 13. Thecorrugating adhesive of claim 2, wherein the adhesive further comprisesan effective amount of borax.
 14. The corrugating adhesive of claim 13,wherein the adhesive comprises about 60 to 95% raw starch, 5 to 40%soluble high amylose starch, and 0.5 to 8.0% borax, based on the dryweight of the adhesive.
 15. The corrugating adhesive of claim 2, whereinthe adhesive further comprises an effective amount of alkali.
 16. Thecorrugating adhesive of claim 15, wherein the adhesive comprises about60 to 95% raw starch, 5 to 40% soluble high amylose starch, and 0.5 to6.0% alkali, based on the dry weight of the adhesive.
 17. Thecorrugating adhesive of claim 2, further comprising a crosslinkingagent.
 18. The corrugating adhesive of claim 17, wherein thecrosslinking agent is a ketone-aldehyde resin.